The present invention relates to a utility knife. More particularly this invention concerns such a knife that holds a disposable razor-type blade by means of a pivotal retainer element.
A utility knife such as described in European patent 0,687,530 of H. Knoop has a housing adapted to be held in the hand and having one end formed with a seat in which a standard isosceles-trapezoidal blade fits with its point projecting from an end of the housing. A cover or retainer pivoted on the housing is movable between a closed position engaging over the blade and holding it tightly against the housing in the seat and an open position permitting the blade to be removed from the seat for replacement or reversal. A spring between the retainer and the housing pops the retainer open when the latch is released, simplifying blade changing or reversal. Another hinged part acts as a latch to hold the retainer in the closed position and is positioned such that during normal use it will not move out of the latched position.
U.S. Pat. No. 5,797,188 of Gilbert discloses a similar such utility knife where instead of a hinged latch, the retainer carries offset from its pivot axis a large-diameter wheel having a threaded shaft that fits into a threaded hole in the housing. This wheel can be rotated to screw its threaded shaft into the hole and thereby solidly secure the retainer to the side of the housing, holding the blade in its seat, and can be unscrewed to free the retainer and allow the blade to be replaced or reversed.
Both of these knives have to be made to relatively tight tolerances to ensure that the parts latch together properly. This is particularly true for the screw-type retainer which must fit together perfectly coaxially to function. Furthermore neither knife holds the retainer so tightly that it cannot be pried open at the front end, for example when cutting with considerable lateral force, so that the blade can come loose or the knife can be damaged.
It is therefore an object of the present invention to provide an improved utility knife.
Another object is the provision of such an improved utility knife which overcomes the above-given disadvantages, that is which is of simple and inexpensive construction yet which very solidly holds its blade.
A utility knife has according to the invention a flat blade formed with at least one throughgoing hole, a housing member forming a seat adapted to receive the blade, and a retainer member engageable with the blade on the seat. A pair of respective pivot elements on the housing and retainer members allow pivoting of the retainer member between a closed position engaging the blade and holding it against the seat and an open position exposing the blade and permitting its removal from the seat. Respective threadedly interengageable holding elements including a threaded screw on one of the members extending through the hole of the blade and a nut on the other of the members secure the retainer member in the closed position.
Thus with this system the screw engaging right through the blade ensures that there is no significant lever action on the retainer member when the knife is used for rough cutting, for instance opening a bag. The blade is solidly held in place, yet can be changed easily simply by unscrewing the nut and screw from each other so the retainer member can be lifted to the open position.
According to the invention the threaded screw is fixed in the housing member and has a threaded shaft projecting up from the seat. The nut is rotatable on the retainer member. The retainer member is formed with a large-diameter recess receiving the nut with radial play. Thus even if the parts do not line up perfectly, the nut can be threaded on the screw. The knife does therefore not have to be made to tight tolerances.
The retainer member in accordance with the invention is formed with a stepped bore aligned in the closed position with the shaft of the screw and having an outer small-diameter portion and an inner large-diameter portion lying in the closed position between the outer portion and the blade. The nut has an internally threaded stem loosely received in the stepped bore and having an inner end with an outwardly projecting ridge of a diameter slightly greater than an inner diameter of the outer small-diameter stepped-bore portion so that the nut is captured by the stem on the retainer member. The nut can therefore move axially and radially of the axis of the screw, and can also tip somewhat relative to this axis to ensure easy fitting together of the nut and screw when the retainer is closed.
The pivot includes a pin fixed on one of the members and defining a pivot axis and a formation on the other of the members engaged around the pin. In accordance with the invention the formation engages with radial play relative to the pivot axis around the pin so that the retainer member can move limitedly radially of the pivot axis relative to the housing member. This also ensures that, even if the retainer and housing do not fit together perfectly, the nut and screw, which are normally made of metal while the rest of the structure is molded of plastic, will be able to align and fit together perfectly. The pivot axis can be transverse or parallel to the housing member.
In accordance with the invention a spring is provided on the housing member for biasing the retainer member into the open position. This spring is a coil compression spring having an inner end fixed to the housing member and an outer end engageable with the retainer member. A screw seated in the housing member has a head pressing the spring inner end against the seat and extends through the housing member and into a cover plate in which the screw is seated.
The seat is recessed in housing member and the retainer member is set generally flush in the housing member in the closed position. The blade has a pair of holes through one of which the screw engages. The seat is formed with a centering bump engaging in the other of the holes.